ADI (Austempered Ductile Iron): Ultra-High-Strength Cast Iron
ASTM A897/A897M · Updated: 2026-05-25
ADI (Austempered Ductile Iron) is ductile iron that has been austempered—heated to 850-900°C, quenched in a salt bath at 250-400°C, and held isothermally to form ausferrite (acicular ferrite + carbon-stabilized austenite). This unique microstructure delivers strength comparable to forged alloy steels (1,200-1,600 MPa tensile) at 20% lower weight and 10-20% lower cost. ADI Grade 3 (highest strength) is used for heavy-duty gears, crankshafts, and suspension components in trucks and construction equipment, replacing forged 4140/4340 steel. ADI Grade 1 (highest ductility) is used for safety-critical automotive components requiring energy absorption. The ausferrite microstructure also provides excellent wear resistance and contact fatigue strength—gear life improvements of 50-200% over conventional ductile iron gears.
Quick Facts
| Category | Cast Iron |
| Standard | ASTM A897/A897M |
| Density | 7.10 g/cm³ |
| Yield Strength | 896-1,100 MPa (130-160 ksi) Grade 3 |
| Tensile Strength | 1,200-1,400 MPa (174-203 ksi) Grade 3 |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN-GJS-1000-5 | Compare |
| ISO 17804 | Compare |
| ADI 1050 | Compare |
| JIS FCD900 | Compare |
| ADI Grade 3 | Compare |
Related Materials
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Frequently Asked Questions
What are the machining considerations for ADI?
ADI is difficult to machine after austempering due to the ausferrite microstructure and strain-induced martensite transformation at the tool tip. All machining should be done on the ductile iron casting before austempering, allowing 0.25-0.5% growth during the process. Finish grinding or hard turning with CBN inserts is viable for tight tolerance surfaces. Design components so that all critical features are machined in the as-cast state before heat treatment.